The present invention relates to component subsystem measurements, and more particularly to the remote estimation of amplifier functionality using a measurement instrument coupled to the amplifier via a transmission medium.
A traditional method of measuring the frequency response of an amplifier is to couple the amplifier's input and output to a network analyzer or similar device, such as a spectrum analyzer with a tracking generator or the like, and to apply a swept frequency signal to the amplifier from the analyzer. The network analyzer measures the output of the amplifier over the swept frequency range and provides a frequency versus amplitude display of the output. This type of measurement is usually performed in a laboratory or shop where the amplifier is easily accessible.
Measuring the response of an amplifier becomes much more difficult when the amplifier is positioned adjacent to an antenna that is not easily accessible. Such configurations are used with telecommunication systems, such as wireless communications systems and the like, deep space satellite antennas, radio astronomy antennas and the like. In a wireless communications system the antenna is generally positioned on a tower, side of a building or the like to provide the maximum coverage area for the antenna. A preamplifier is mounted in a weather-proof box close to the antenna and is coupled to receive the signal from the antenna. The preamplifier amplifies the signal and couples the signal out of the box via a transmission cable, such as a coaxial cable, to a base station remote from the antenna. The cable enters the base station and may be connected via a jumper cable directly to an equipment rack that generally has a tap for connecting test equipment to the transmission cable. Power for the preamplifier is provided from the equipment rack. Alternatively, a jumper cable may connect the transmission line to a junction box that receives an alternating current (AC) voltage input. The AC voltage is converted to direct current (DC) voltages for powering the preamplifier. A second jumper cable connects the junction box to the equipment rack.
Measuring the parameters of the preamplifier in situ at the top of an antenna tower currently requires a technician to climb the tower with a portable network analyzer or the like. The technician opens up the weather-proof box containing the preamplifier and disconnects it from the antenna and transmission cable, connects the network analyzer to its input and output, and measures its frequency response. After completing the test the technician reconnects the amplifier to the antenna and transmission cable, reseals the weather-proof box and descends the tower.
There are a number of drawbacks to the above method of determining the functionality of a preamplifier mounted adjacent to a remote antenna. The first is that the weather-proof box has to be opened when testing the preamplifier. Generally, once the box is opened the weather-proof integrity of the box is compromised. It is very difficult to completely reseal the box to prevent ingress of moisture into the box. Second, the technician authorized to make the measurement may not be the same technician that supports the base station. Thus, it requires more than one individual to maintain the antenna and base station. This results in added overhead. Further, company and/or government safety requirements may dictate that special equipment, emergency support, special training and the like be used and provided for anyone climbing the tower. Again, this adds costly overhead to the operation of the tower and base station.
What is needed is a method of estimating the functionality of an amplifier that is remotely located from a measurement instrument.